The present invention relates to propulsion and control of underwater vehicles, more particularly to dual-propeller-based systems for accomplishing same with regard to submersibles such as unmanned underwater vehicles (UUVs).
Current methodologies for underwater propulsion and control require multiple systems in order to provide efficient cruise power and low-speed control. Conventional rigid propellers afford good thrust but poor lateral and off-axis control (i.e., control of lateral forces and moments). Conventional underwater vehicles seek to overcome such deficiencies by implementing additional devices, e.g., rudders and planes for lateral control. Rudders and planes, however, are ineffective at low speeds or while hovering. Although thrusters can be implemented to provide multi-axis control, they require axis-independent units and are not suited for high-speed or high-efficiency applications.
Frederick R. Haselton introduced about fifty years ago, and subsequently developed, his basic concept of an underwater vehicle propulsion-and-control system involving a pair of fore-and-aft coaxial contra-rotating propellers. Haselton sometimes referred to his concept as the “Tandem Propeller System,” or “TPS.” Haselton taught the coordinated control of the “cyclic” and “collective” blade pitch of the blades on each propeller in order to propel and maneuver his vehicle, in his words, “in six degrees of freedom.” Cyclic blade control changes the pitch angle of each propeller blade in accordance with the blade position in a cycle (one complete blade rotation about the propeller hub); every blade changes its pitch angle to the same degree at the same point in the cycle. Collective blade control changes the pitch angle of all of the propeller blades equally and simultaneously, and independently of the blade position. Haselton originally disclosed electromechanical blade pitch control, and later disclosed electronic blade pitch control.
The term “six degrees of freedom” is conventionally used to describe both translational motion and rotational motion of a body with respect to three perpendicular axes in three-dimensional space. In general, a marine vessel is characterized by motion describable in terms of six degrees of freedom, viz., heave, surge, sway, roll, pitch, and yaw. The three kinds of translational ship motion are commonly referred to as heave (linear movement along a vertical axis), surge (linear movement along a horizontal fore-and-aft axis), and sway (linear movement along a horizontal port-and-starboard axis). The three kinds of rotational ship motion are commonly referred to as roll (rotational movement about a horizontal fore-and-aft axis), pitch (rotational movement about a horizontal port-and-starboard axis), and yaw (rotational movement about a vertical axis).
Pertinent to the instant disclosure are the following United States patents to Haselton, each of which is incorporated herein by reference: Frederick R. Haselton, U.S. Pat. No. 3,101,066, issued 20 Aug. 1963, entitled “Submarine Hydrodynamic Control System”; Frederick R. Haselton, U.S. Pat. No. 3,291,086, issued 13 Dec. 1966, entitled “Tandem Propeller Propulsion-and-control System”; Frederick R. Haselton et al., U.S. Pat. No. 3,450,083, issued 17 Jun. 1969, entitled “Submarine Hydrodynamics Control System”; Frederick R. Haselton, U.S. Pat. No. 3,986,471, issued 19 Oct. 1976, entitled “Semi-Submersible Vessels”; Frederick R. Haselton, U.S. Pat. No. 4,054,104, issued 18 Oct. 1977, entitled “Submarine Well Drilling and Geological Exploration Station”; John L. Wham et al., U.S. Pat. No. 4,648,345, issued 10 Mar. 1987, entitled “Propeller System with Electronically Controlled Cyclic and Collective Blade Pitch.”
As evidenced by the above-noted patents to Haselton, the concept of a cyclically and collectively controllable propulsor for effecting vectored thrust in a marine power system has been known for some time. Other literature disclosing cyclic and collective blade pitch control of a marine propeller includes the following two U.S. patents, each incorporated herein by reference: Frank B. Peterson et al., U.S. Pat. No. 5,028,210, issued 2 Jul. 1991, entitled “Propeller Unit with Controlled Cyclic and Collective Blade Pitch”; William E. Schneider, U.S. Pat. No. 5,249,992, issued 5 Oct. 1993, entitled “Marine Propulsion Unit with Controlled Cyclic and Collective Blade Pitch.” In addition, the skilled artisan who reads the instant disclosure will be familiar with the well-known practices and plethora of literature relating to cyclic and collective blade pitch control in helicopters and other rotor aircraft.
The United States Navy has investigated over many years the generation, through the use of non-articulating variable-pitch blades, of control and translation forces and moments in marine vessels. See, e.g., H. Weiner, “Conceptual Design and Model Investigation of the Propulsion, Stability and Control Characteristics of a Small Tandem Propeller Submarine (TPS Scheme B,” Report 416-H-01, David W. Taylor Naval Ship Research and Development Center (now known as the Naval Surface Warfare Center, Carderock Division, or “NSWCCD”), Bethesda, Md. More recent work (such as by Benjamin Y.-H. Chen, Stephen K. Neely, Kurt A. Junghans, and David P. Bochinski of NSWCCD, and David C. Robinson of the U.S. Naval Academy) has focused on investigating the application of these concepts to small UUVs. A recent prototype according to Y.-H. Chen et al. has demonstrated significant improvements in control at low speeds, but has also demonstrated significant limitations with respect to sideward translational motion.